Accumulator for hydraulic systems



Feb. 5, 1957 R. G. SHARP ETAL 2,780,064

ACCUMULATOR FOR HYDRAULIC SYSTEMS Filed Nov. 10, 3.953 2 Sheets-Sheet lAccumulator Robert 6. Sharp a Howard .E. Wright INVENTORS ATTORNEY Feb.5, 1957 R. G. SHARP ET AL 2,780,064

ACCUMULATOR FOR HYDRAULIC SYSTEMS Filed NOV. l0 1955 2 Sheets-Sheet 2,//4 44 56 ff Fig. 3 55 r 45 55 59 M 52 22 Roberf 6. Sharp 8: Howard E.Wright INVENTORS A T TORNE Y United States Patent ACCUMULATOR FORHYDRAULIC SYSTEMS Robert G. Sharp, San Diego, and Howard E. Wright, LaMesa, Califi, assignors, by mesne assignments, to General DynamicsCorporation, a corporation of Belaware Application November 10, 1953,Serial No. 391,226

11 Claims. (Cl. 60-51) The present invention relates generally tohydraulic actuating systems and more particularly to improved componentsof closed type hydraulic actuating systems.

The present invention is directed to improved hydraulic systems andcomponents thereof wherein a novel constant pressure type accumulatorprovided with multiple chambers and pistons is pressurized by acompressed air source which serves to develop a high pressure actuatingfluid medium and a relatively low pressure circulating fluid medium withautomatic means for providing makeup fluid for the high pressure medium.The improved hydraulic system is of the closed type and includes inaddition to the novel constant pressure pump type accumulator, asuitably powered circulating pump, a bypass valve in the pump circuit, aservo control valve and the actuating cylinders or motors, in additionto the customary accessories of such systems comprising pressureregulators, relief valves, filters, etc. The present hydraulic system isparticularly adapted for the actuation of the control surfaces ofaircraft and other vehicles and the characteristics and advantages ofthe improved system and its components are. especially adapted for theactuation of the control surfaces or other movable portions of guidedmissiles and the like.

It is, accordingly, a major object of the present invention to providean improved hydraulic system of the closed type. It is a corollaryobjective to provide improved components of such closed hydraulicactuating systems, as well as a novel and advantageous relationship ofthose components. It is a. further object of this invention to providean improved hydraulic system and its components for the actuation of thecontrol surfaces of aircraft and guided missiles. A further object ofthe invention resides in the provision of a hydraulic system which ispneumatically charged from a propellant source and which develops a muchhigher hydraulic actuating pressure, the volume and replenishment ofwhich is automatically maintained by a power-driven circulating pump ina low pressure hydraulic circulating portionof the system.

It is a further object of the present invention to provide an improvedair driven automatic pump type accumulator which through the use ofdifferential area pistons converts low pressure air into higher pressurehydraulic fluid or oil. A further object is to provide a high outputhydraulic system which may be installed in a minimum of space, which isfree from oil flow pulsations and is self-replenishing. It is a furtherobject to provide a hydraulic system in which the rate of deliveringenergy is not limited by the size of the unit, a system which has theadvantage of not causing electrical interference with other componentsof the vehicle, one which may be. used in explosive atmospheres and doesnot require cooling. It is a still further object to provide an improvedhydraulic system of the type described and more particularly an improvedmultiple piston type accumulator and a novel inter-relationship of thesame with the other components of the hydraulic system.

Other objects and advantages of the present invention will occur tothose skilled in the art, after reading the following description takenin conjunction with the accompanying drawings, forming a part hereof, inwhich:

Fig. l is a diagrammatic view of a form of the improved hydraulicsystem;

Fig. 2 is an end elevational view to a larger scale of the improvedaccumulator forming an essential component of the system of Fig. 1;

Fig. 3 shows a cross-sectional view of the improved accumulator as takenalong the lines 3-3 of Fig. 2;

Fig. 4 is an enlarged cross sectional view of the by-pass valveassociated with the accumulator, .as taken along the lines 44 of Fig. 2;

Fig. 5 is a further cross-sectional view of the by-pass valve of Fig. 4as taken along the lines 5-5 of Fig. 2; and

Fig. 6 is a cross-sectional view of the by-pass valve of Figs. 4 and 5as taken transversely along the lines 6-6 of Fig. 4.

Referring now to Figs. 1 to 3, inclusive, the improved accumulator isindicated generally by the numeral 10 and comprises a normally balancedpiston type device having a fixed casing 40 provided with a largecylindrical bore 43 in which is reciprocably mounted the primary or maindifferential area piston 55. The accumulator also has a secondary orsmaller bore 45 within which is reciprocably mounted the double innerdifferential area piston 54 which may be referred to as the secondary orcontrol piston. The accumulator 10 is activated or charged by compressedair from the air tank or receiver 11, which air enters the accumulatorat the air inlet F and is interposed between the primary and secondarypistons 55 and 5-1 respectively, to develop a high pressure workinghydraulic fluid on the outside working face: 56 of the primary piston 55exerted through the ports L, L1 and L2 due to the differential areas ofthe exposed portions of the piston 55. The actuating air also exerts anopposite inward force upon the secondary piston- 50 which develops a lowpressure in the circulating control hydraulic fluid within the sumpchamber S having the sump ports D, E, and H. In its normally balancedstate, and in a preferred form of the accumulator due to thedifferential areas of piston 55 at which an air pressure ofapproximately 480 p. s. i. is admitted through the port F into thechamber G, a hydraulic fluid working. pressure of 1500 p. s. i. isdeveloped within the chamber K and is available through the ports L, L1and L2. Under the same balanced conditions, and also due to diiferentialareas, the compressed air at 480 p. s. i. exerted on the smaller exposedarea of the secondary piston 50 develops on the larger area pistonportion 52 a pressure of 20 p. s. i. in the circulating con trolhydraulic fluid. As will be more particularly described hereinafter, theprimary purpose of the low presure fluid within the sump S of theaccumulator is to provide for fluid return from the servo control valve25 and also to cooperate, through a circulating portion of the systembetween the ports D and E in cooperation with theby-pass valve 18, toprovidemake-up fluid in the high pressure. working portion of the systemto compensate for leakage or other loss of Working fluid.

As will be noted by reference to Fig. 1, the compressed air is storedwithin, and is supplied from, the air tank or receiver 11, passingthrough the air filter 12, the hand arming valve 13 and through the airline 14 to the pressure regulating valve 15- which reduces and controlsthe pressure of the air passing therethrough to an air pressure of 480p. s. i. From the pressure regulating valve 15 the compressed air iscarried by the air line 14 through the air inlet port F and to theannular passages G between the inside of the primary piston 55 and thefixed outer limits of the outer chamber K or the bore 43, through whichpassages the air pressure enters the main chamber G and is exerted uponthe large inner area of the primary piston 55 and the small inner areaof the secondary piston 50. One of these annular passages communicatesthrough the connection 60 with an air relief valve 61 which is normallyset to open to the atmosphere or other open space at a pressure of about550 p. s. i. A large internal chamber M is formed between the fixed endplate or plug 46 of the bore of inner cylinder 45 and this chamber M isopen through the port 54 to the atmosphere or to a suitable ventconnection. The low hydraulic pressure within the sum S (on the rightside of piston 5052 as viewed in Fig. 3) is therefore opposed only byatmospheric pressure on the inner or left face of the large end of thesecondary piston 52 exposed to the atmospheric chamber M and by theactuating or charging air pressure within the chamber G exerted upon theinner and smaller end areas 51 and 51a of the secondary piston portion50. It will be understood that the compressed air receiver 11 may be ofany suitable shape to withstand the compressed air pressure (in excessof 480 p. s. i.) and that it is particularly suited in the case ofguided missiles, rockets and the like, to be disposed in otherwiseunoccupied space or to be formed by the shell of the missile, or aportion thereof.

Referring now more particularly to the details of the improvedaccumulator 10 as shown in Fig. 3, and the supplementary figures, thefixed portion of the accumulator casing comprises an outer annularcasing member 40 internally bored as at 43 to form chamber K for thepiston portion 56 of the primary piston 55. The fixed casing head orplate 41 engages the annular casing member 40 in a rotationally lockingbayonet type joint 42 provided with a locking bolt 41:: which maintainsthe casing portions 40 and 41 in their locked position. As indicatedabove, the outer casing 40 is apertured for the high pressure ports L,L1 and L2, and is provided with an inwardly facing seal 44 adjacent itsopen end to provide a'liquid-tight seal between the end of the casingportion 40 and the main outer surface of the cylindrical wall of theprimary piston 55. This flanged portion of the casing 40 is alsosuitably tapped to receive the mounting bolts 18a for attachment of theby-pass valve 18 which will be described further below. The fixed casinghead 41 is provided with the ports D, E, and H, all in communicationwith the sump S, as well as the port F for connection to the chargingair pressure line 14, and the passageway 60 for the, relief valve 61.The casing head 41 is also provided with a cylindrical wall portioninternally bored as at 45 to define the atmospheric chamber M to whichcommunication is provided through the passageway 54. The inner end ofthe cylindrical bore portion 45 is closed by the apertured end plug 46having its periphery attached to the cylindrical wall portion 45 andsuitably sealed thereagainst at 47, and with its internal bore suitablysealed at 48 to provide fluid-tight contact against the outercylindrical surface of the secondary piston portion 50. The end plug 46is locked in position within the cylindrical wall portion 45 by theapertured retaining ring 49 through the central opening of which thecompressed air is free to flow to all portions of the chamber G.

The inner or secondary multiple piston 50 is provided with a fixed joint50a by which the inner end 51a of the piston 50 is secured to the wallof the large piston portion 52. The latter is provided at its peripherywith the fluid seal 53 for sliding engagement with the bore 45 and theouter end 51 of the small piston 50 is slidingly sealed within themember 46 by the ring seal 48, as indicated above. The outer or primarypiston assembly 55 is provided with the small area shouldered workingpiston portion 56 reciprocable within the cylinder bore 43 against whichit is sealed by the peripheral seal 57. The central portion of theprimary piston assembly 55 is provided with the plug fitting 58threadedly engaging the threaded opening in the portion 55 at thethreads 59, the plug 4 fitting 58 being provided with an internal boreforming an extension of the chamber G into which the end 51 of thesecondary piston portion 50 is permitted to move under certain operatingconditions of the accumulator. The casing portion 40 is also suitablybored at its lower portion to permit passage of the piston rod 69disposed within the chamber K and in contact with the piston portion 56.

Referring again to Fig. 1, there is disclosed a preferred form of aservo system to which the improved accumulator 10 is particularlyadapted. In the portion of the system which is discloseddiagrammatically for illustrative purposes, there is provided the servocontrol valve 25 to which suitable control forces may be applied. In thecase of a control system for a guided missile, these forces may beapplied by such automatic control components as a gyroscope, radiocontrol or electronic instrumentalities, or in other vehicles by thehuman pilot, or the automatic substitute therefore. The component to bemoved or controlled is suitably connected to the piston rod 35 of thepiston 34 of the hydraulic servomotor 30. For illustrative purposes thepiston 35 is shown pivotally connected to the control arm 71 of thecontrol surface 72 pivotally mounted at 73. The actuating cylinder ormotor 30 may preferably be of the double area type with the small areapiston side of the cylinder 33 supplied by high pressure workinghydraulic fluid at 1500 p. s. i. through the conduit 31 connected to theport L of the accumulator 10 and the opposite portion of the cylinderexposed to the large area face of the piston 34 (which is uninterruptedby the piston rod 35) connected through the conduit 32 with the servocontrol valve 25. In this type actuating cylinder, the servo valveselects the large area from pressure to return, thus controlling themovement of the actuating piston 35 of the motor.

The servo control valve 25 is actuated by the push-pull link 26 suitablyconnected to the pilot instrumentality and pivoted at 26a to the rockinglink or lever 26b in turn connected to the valve piston 36 and rockablymounted upon the casing of the valve 25 by the pivot 260. The valvepiston 36, preferably having four land portions, is reciprocably mountedwithin the cylindrical bore of the chamber 37 the ends of which arevented to the atmosphere by the passages 25a. Operating fluid issupplied to the valve from the high pressure chamber K of theaccumulator 10 through the port L1 and the conduit 27 at the workingpressure of 1500 p. s. i. which is also transmitted through the conduit31 to the servomotor 30. By means of the pressure-reducing valve 28,however, this pressure is reduced to 450 p. s. i. at which it isconducted through the continuation of the conduit 27 to the centralportion of the chamber 37 of the valve 25. The latter is also providedwith a further cylindrical chamber 39 within the bore of which isreciprocably disposed the second valve piston 38. The latter is providedwith three land portions which are normally centrally disposed in abalanced condition by means of end centering springs, or similarresilient means, and the central land normally covers the portcommunicating with the conduit 32 extending to the large area side ofthe piston 34 of the servomotor 30. The valve piston 38 accordinglydivides the chamber 39 into two end portions, one of which is open tothe high pressure conduit 29from the outlet port L2 of the accumulator10 conducting hydraulic fluid at 1500 p. s. i. into this end chamber,whereas the opposite end chamber is open to the return line 22 to thereturn port H to the sump S of the accumulator 10 by means of theconnection 24 from the valve 25. The piston valve 36, provided with fourland portions, forms a central chamber open to the 450 p. s. i.hydraulic line 27 and a pair of end chambers which communicate throughthe return line 23 with the main return line 2224 connected to theopposite side of the valve 25 and to the accumulator 10. g g

The operation of the servomotor 30 by the servo coin trol valve 25 inconjunction with the improvedaccurnulator is accordingly as follows:Assuming that a pilot force is exerted upon the actuating link 26 tomove the pivot 26a to the position indicated by the letter U, the pistonvalve 36 is drawn to the left by the link 26b and the hydraulic fluid ata pressure of 450 p. s. i., which enters the central chamber from theconduit 27, is permitted to pass downwardly through the channel in thecasing of the valve to the left end of the valve piston 38. Movement ofthe valve piston 38 to the right in Fig. 1 is thereby initiated andaccordingly the center land exposes or opens the port to the conduit 32,permitting high pressure fluid from the conduit 29 to pass through theleft portion of the chamber 39 and out through the conduit 32 to thelarge area side of the piston 34 thereby overcoming the smaller force atthe same pressure exerted at the opposite side of the piston. This movesthe piston rod 35 downwardly or outwardly from the casing 33 of themotor 30, to thereby actuate the control instrumentality, such as acontrol surface 72 or other component, to the desired extent. At thesame time the fluid which is displaced from the right end of the chamber39 by movement of the valve piston 38 to the right is transmittedupwardly through the passages and outwardly through the return line 23and thence to the main return line 22 and back to the accumulator 10through the port H. With the return of the link 26 to its normal or itsneutral position as shown in full lines in Fig. l, the valve pistons 36and 38 again become centralized in their normal balanced positions. Onthe other hand, however, should the actuating link be drawn to the leftsuch that the pivot 26a is moved toward the position V, the valve piston36 is moved toward the right and the fluid pressure from the conduit 27and the central portion of the chamber 37 passes to the right end of thechamber 39 causing the valve piston 38 to move to the left to cause theconduit 32 from the servomotor to be placed in communication with thereturn line 24 through the right portion of the chamber 39. This causesa corresponding reduction in pressure on the face of the piston 34causing it to be withdrawn further within the cylinder 33 and causes thecomponent 72 attached to the piston rod to be moved in the oppositedirection to the desired extent. At the same time, the fluid which isdisplaced by the movement of the valve piston 38 to the left ispermitted to be placed in communication with the return line 24. Whereasbut a single servomotor 38 has been shown and described, it will beunderstood that a plurality of such motors may preferably be provided inthe control system with suitable servo control valve connectionsthereto.

Referring now to Figs. 3 to 6, inclusive, there are shown the detailsand operation of the low pressure circulating system and the novelby-pass valve 18 which cooperate with the improved accumulator 10 toprovide make-up fluid to the working side of the system in the event ofleakages, or due to other losses. On the low pressure hydraulicfluidside of the accumulator 10, the port E supplies fluid from the sumpS through the conduit 16 to the continuously operating motor drivenfluid pump 17. This circulating pump delivers hydraulic fluid throughthe discharge portion of the conduit 16 and into the bypass valve 18through the normally open port A. As shown inFigs. 3 and 4, under normalbalanced operating conditions of the accumulator It), the port A is openthrough the intermediate passageway C to the outlet B of the bypassvalve 18 from which the circulating fluid at a pressure of approximately20 p. s. i. passes into the conduit 21 and is returned through the inletport D to the sump S of the accumulator. The pump 17, under certainoperating conditions, is capable of developing pressures in excess of1500 p. s. i. when its discharge is restricted or opposed and as arelease of excessively high pressures a relief valve 20 set to crack oropen at about 1750 p. s. i.

is disposed across the pump 17 to relieve the high pressure dischargethrough the relief line 19 back to the sump S or to the suction side ofthe pump. The actuating connection between the three-chamber accumulator10 and the by-pass valve 18 is the above-mentioned rod 69 within thehigh pressure chamber K in contact with the outer cylinder portion 56.

The bypass valve 18 comprises essentially a casing or block ofrectangularcross-section provided with a plu rality of longitudinalbores parallel to the axis of the rod 69 and the central axis of theaccumulator 10. The valve body 18 is provided with the bore R withinwhich the enlarged sealed piston portion 70 of the rod 69 is adapted toreciprocate as the piston portion 56 of the accumulator moves in theaxial direction within the bore 43 of the outer chamber K. The oppositeend of the bore R is closed by the threaded plug 68 and parallel to thebore R there is provided a larger and also parallel bore 65, the endportions of which are connected to the bore R by the oblique channels orpassages R1 and R2. Within the bore 65, thereis disposed a movablepiston element 62 having a shank portion slidingly fitted within thefixed piston guide fitting 63 which is retained in the valve casing bythe retainer disc 64. The opposite end of the piston element 62 isprovided with a necked valving portion 62a arranged to slidingly fitwithin the aligned but smaller bore 66 in alignment with the axis of thelarger bore 65. The enlarged valving portion 62a of the valve piston 62is normally disposed, as shown in Fig. 4 between the above-mentionedport A through which the pump 17 discharges and an adjacent port P whichalso extends transversely of the bore 66 and communicates with a furtherlongitudinal passage T, as shown in Fig. 5. The outer end of thepassageway T is in fluid communication by means of the inclined passageT1 with one or more of the radially extending ports Q of the pistonguide fitting 63. The contacting end surfaces of the by-pass valve body18 and the outer casing member are squared and well finished, and areprovided around :the openings for the rod 69 and the passage T withsuitable seals to prevent leakage through the joint of the high pressureworking fluid. accumulator 10 in which the several fluid pressures arein balance, the outer piston is substantially telescoped within thefixed casing portion 40, and the rod 69 and its piston portion 70 aremaintained in contacting relationship with the piston portion 56 asshown in Figs. 3 and 4 by virtue of the greater pressure exerted uponthe ex posed end of the piston portion 70 a compared to the smaller endin contact with the piston 56 and the shoulder of the piston 70 which is:open to the low pressure of the circulating port C. The end of thelatter port is closed by the plug 67a.

When, however, any loss of working fluid or drop in pressure occurs onthe high pressure side of the accumulator, the pressure of thecompressed air maintained within chamber G automatically recharges thehigh pressure chamber K and the high pressure side of the accumulator inthe following manner. When a reduction in volume occurs (in a preferredform of the accumulator this has beenestablished as a loss of six cubicinches equivalent to a position extension from its normal position ofapproximately .63 inch) the outer piston 56 moves outwardly of the outercasing 49 away from the end plate 41 to a position at which the piston70 on the rod 69 reaches the position W, in Fig. 4. In the full lineposition of the control piston 70, as also shown in Fig. 4, it will beseen that the high pressure fluid which reaches both ends of the chamberthrough the channels T, T1 and P also reaches the bore R and both endsof the larger bore 65 through the passages R1 and R2. The greater fluidpres sure on the enlarged piston of the piston element 62 causes it tooccupy its retracted position as shown in the full lines in Fig. 4 inwhich its valving portion 62a is disposed between the pump dischargeport A and the transverse port P and the low pressure circulating fluidfrom Under the norm-a1 operating conditions of the.

the pump 17 passes through the open port A, the. passage C and theoutlet B into the conduit 21. When, however, the control piston 70 ismoved to, the dotted position W due to loss of fluid or pressure on thehigh pressure side of the accumulator, the trailing or shoulderedportion of the piston 70 reaches the transverse passage R1 cutting offthe adjacent end of the chamber 65 from the high pressure fluid andrelieving the residual pressure within this portion of the chamberthrough the passage Rl around the rod 69 and into low pressure passagesC and B. As the fluid pressure on the adjacent side of the piston 62 isreduced, the high pressure which is still maintained on the outer end ofthe piston within the guide 63, causes the same to move toward theaccumulator with the result that the port P is placed in communicationwith the port A by the valving portion 621: of the piston reaching thedotted line position, indicated at Y in Figs. 4 and 5. This causes thecirculating flow from the. pump 17 to the sump S through, the line 21 tobe interrupted and it opens the pump discharge to the high pressurethrough the passage P. The pump 17, accordingly, picks up its load andimmediately develops pressures in exces of that imposed upon itsdischarge by the fluid passing from the passage P through the port A inthe direction opposite to the normal flow and the increased pressuregradually causes the outer piston 55-56 to telescope within the outercasing portion 4-9 and to return the primary piston 55 56 toward the endcasing head 41 to its normal operating position. As the piston portion56 again telescopes or return it is followed by the control rod 69 andits piston 70 due :to the increased pressure on the outer end of thepiston 70 until the latter finally resume-s its initial position asindicated by the full lines in Figs. 3 and 4. When this occurs, the highpressure fluid again is permitted to enter the transverse passage R1 andthe piston 62 is caused to move outwardly again to its normal positionwith the residual air displaced from the mid-portion of the chamber :65being displaced to the atmosphere through the vent passageway 65a. Asthe piston again moves outwardly, telescoping within its guide fitting63, its valving portion 62a passes over and outward of the inlet Acutting off its connection to the high pressure fluid through the port Pand causing the pump to again discharge in its normal low pressurecirculating flow-path through the passage C, the passage B and throughthe conduit 21 back to the sump. S. If during this recharging process,the pressure developed on the high pressure side of the system shouldexceed 1750 p. s..i., the, relief valve 20 opens and the excess fluid isreturned through the line 19 to the suction or low pressure side of thepump 17 comprising its sump S and the suction portion of the line 16.

It will, accordingly, be seen that the improved accumulater and itsmakeup by-pass valve 18 form an essential portion of a hydraulicactuating system which i charged from a compressed air receiver and isautomatically maintained in operating condition with the desiredactuating pressures by means of a continuously running hydraulic pumpwhich delivers hydraulic fluid at a rate in a preferred embodiment, ofapproximately 1 gal. per minute with the requirement of but relativelylow power input. This is accomplished by the improved accumulator whichis made up of three telescoping chambers, namely, an outer high pressurechamber K, an intermediate or compressed air charging chamber G and aninner :or low pressure sump chamber S, with a supplementary atmosp'heric cnamber M disposed between chambers G and S. The system is alsosuch that the working fluid on the high pressure side of the accumulatoris automatically returned through the servo control valve followingactuation of the servomotor and when the pressure or volume of fluid onthe high pressure side is reduced to a predetermined extent, it isautomatically replenished from the return sump of the accumulatorthrough the continuously running pump 17 as determined by thepositioning of the actuating-elements 69-70 of :the bypass valve 18which reflectsthe condition of; the several telescoping chambers in theaccumulator. 1.0..

The improved accumulator is also in effect an air driven automaticreciprocating hydraulic pump which is automatically controlled. andprovided with make-up fluid by the. small continuously runningcirculating pump. The improved system compares favorably with the moreconventional, electric motor pump system and the one shot accumulatorsystem and is admirably adapted to withstand high acceleration forcessuch as particularly met with in rocket and missile operations. It maybe operated as described, by energy stored in the form of compressedgas, which may either be air, nitrogen, carbon, dioxide, etc, and thisgas may be stored at a high pressure and furnished to. the unit at thereduced pressure held constant by the pressure regulator. Whereas theconstant pressure air will normally deliver constant pressure hydraulicfluid or oil, the present system is not limited to constant operationbut through the use of differential area pistons, the energy of lowpressure air is converted into much higher pressure hydraulic oil. Thedescribed system is particularly adapted for high output hydraulicsystems for installation in a minimum of space and in such systems thepresent accumulator is ideal for supplying hydraulic oil at variablevolumes. The improved accumulator overcomes many of the disadvantages ofthe conventional accumulator in that the supply is not limited by size,and also in that the working pressure does not drop as the oil is usedor lost, and in effect the improved accumulator provides the moredesirable characteristics of a self-replenishing accumulator operatingat constant pressure. When an electric motor-pump system is designed toapproach the requirements of constant pressure and self-replenishment,it must be designed to accommodate the maximum delivery specificationsof the pump, and if the pump output is to be exceeded even momentarily,an accumulator must be incorporated. As the periods of high flow becomelonger and the flow much greater than the pump output, a duty cycle mustbe defined which limits the periods during which oil is taken from theaccumulator and the periods during which the pump restores theaccumulator charge. Similarly when the demands of thesystem are belowthe pump output, fluid must be unloaded or by-passed and this results ina waste of stored energy. Design parameters of maximum and minimum, useare extremely ditticult to establish for such hydraulic systems,particularly where the system is used for surface control in missileflight. To provide an electric pump system to allow for these variableconditions, results in considerable bulk and weight.

The presently disclosed system meets these variable requirementssatisfactorily and eliminates the drawbacks and shortcomings of theconventional hydraulic systems used heretofore in applying a charge ofair to one side of the system pressurizing the operating oil on theother side, whereas the present device acts as a piston type accumulatorand the stored energy is used only as fast as required by the oildemands. However, high flow requirements can be filled automatically,instantaneously and completely, and load variations are followed withoutthe objectionable replenishing and unloading or by-passing cyclesinherent in prior motor systems, which were also very susceptible, toleakages and pressure losses under the severe conditions, met. with inmissile operation. The improved system is relatively free from oil flowpulsations, obviating the need of surge chambers and automaticaily andrapidly compensates for system oil volume weighty batteries which mustbe supported upon additional structure. It further has the advantages ofhaving its rate of delivering energy nrt closely limited by the size ofthe unit, it has the advantage of no electrical interference, it may beused in explosive atmospheres and it does not require cooling. Any twofluids may be used, either liquid or gas, and the pressure ratios can becontrolled by the piston area ratios. Constant output pressure can beachieved by holding inlet pressure constant and the rates will begoverned by output consumption. Applications other than the specifichydraulic system outlined, will become obvious to those skilled in theart after reading and understanding the foregoing descrip tion. Forexample, it may be advantageously used as a fuel transfer or boosterpump particularly in view of its being explosion-proof and self-cooled.When used as such a pump, compressed air may be supplied from aconvenient remote location or ram air flow from the speed of theairplane or missile might be utilized as well as the circulating engineoil for the working fluid.

Other forms and modifications of the present invention, both in respectto the general system and its components, which occur to those skilledin the art after reading the foregoing description, are intended to comewithin the scope and spirit of the present invention, as moreparticularly set forth in the appended claims.

We claim:

1. An accumulator device comprising a casing having an outer annularhigh pressure chamber and an inner low pressure chamber co-axiallydisposed internally of said outer annular chamber, a primary pistonhaving opposed first and second faces reciprocable within said outerchamber, a secondary piston of lesser diameter than said primary pistonreciprocable within said inner chamber, said primary piston having amajor portion of a first face exposed to the atmosphere and theremaining portion of said first face exposed to the interior of saidouter chamher, and port means extending through said casing foradmitting charging fluid at a pressure intermediate the pressures withinsaid outer and inner chambers to an interior space disposed between thesecond face of said primary piston and said secondary piston whereby ahigher pressure is applied by said charging fluid acting against theentire second face of said primary piston to the fluid in said outerannular chamber and a lower pressure is applied to the fluid within saidinner chamber.

2. An accumulator of the type called for by claim 1 characterized bysaid inner low pressure chamber having ports arranged to deliver fluidto and receive fluid from a circulating pump means and automatic meansinitiated by loss of fluid from said outer high pressure chamber andpredetermined movement of said primary piston to cause delivery of saidpump means to be diverted to said outer high pressure chamber.

3. An accumulator device comprising a fixed casing having an outerannular chamber and an inner cylindrical chamber, said casing having anopening in an end adjacent said annular chamber, an oflset primarypiston reciprocable Within said outer chamber and having an offsetportion projecting through said end opening of said casing wherebydifferential areas of a first face of said primary piston are exposed tothe atmosphere and to said outer chamber, said inner chamber defined byan internal cylindrical wall internally of and of lesser diameter thansaid outer chamber and an internal transverse wall having an openingtherein, a secondary piston reciprocable Within said inner cylindricalchamber and having a reduced diameter portion extending from a firstface through the opening in said internal transverse wall forming adifferential area piston, and port means extending through said casingfor admitting charging fluid at a pressure intermediate those withinsaid inner and outer chambers to an interior space between said primaryand secondary pistons in contact with said second face of said primarypiston and the reduced diameter portion of said secondary "10 pistonwhereby due tothe differential areas of said pistons a higher workingpressure is developed Within the. fluid in said outer annular chamber bythe first face of said primary piston and a lower pressure fluid ismaintained within said inner cylindrical chamber by the second face ofsaid secondary piston.

4'. An accumulator device comprising a fixed casing having first andsecond chambers formed therein, said first chamber adapted to have arelatively higher pressure developed therein as compared to a lowerpressure within said second chamber, a primary piston reciprocablewithin said first chamber, a secondary piston reciprocable within saidsecond chamber, said pistons having differential areas on their workingfaces and port means extending through said casing for admittingcharging fluid at a pressure intermediate the higher and lower pressuresof said first and second chambers to an interior space between theopposed faces of said primary and secondary pistons whereby a pressnreworking fluid higher than said intermediate pressure is developed on theopposite face of' said primary piston and a control pressure lesser thansaid intermediate pressure is developed on the opposite face of saidsecondary piston.

5. In an accumulator system, a fixed casing having a high pressurecylindrical chamber, a primary piston reciprocable Within said highpressure chamber, said casing having a low pressure cylindrical chamber,a secondary piston reciprocable within said low pressure chamber, theadjacent faces of said pistons defining with said casing an intermediatechamber, and a port through said fixed casing for admitting chargingfluid to said intermediate chamber, said primary and secondary pistonshaving differential areas exposed to said charging fluid and to saidhigh and low pressure chambers arranged in such manner that saidcharging fluid causes said primary piston to develop working pressuresin said high pressure chamber in excess thereof and said secondarypiston maintains pressure in said low pressure chamber of lessermagnitude than said charging pressure.

6. In an accumulator system, a fixed casing having a high pressurecylindrical chamber, a primary piston reciprocable within said highpressure chamber, said casing having a low pressure cylindrical chamber,a secondary piston reciprocable within said low pressure chamber, theadjacent faces of said pistons defining with said casing an intermediatechamber, a port through said fixed casing for admitting charging fluidto said intermediate chamber, said primary and secondary pistons havingdifferential areas exposed to said charging fluid and to said high andlow pressure chambers arranged in such manner that said charging fluidcauses said primary piston to develop working pressures in said highpressure chamber in excess thereof and said secondary piston maintainspressure in said low pressure chamber of lesser magnitude than saidcharging pressure and automatic means including a continuously operatingcirculating pump in circuit with said low pressure chamber forautomatically supplying makeup fluid to said high pressure chamber.

7. In an accumulator system, a fixed casing having a high pressurecylindrical chamber, a primary piston reciprocable within said highpressure chamber, said casing having a low pressure cylindrical chamber,a secondary piston reciprocable within said low pressure chamber, theadjacent faces of said pistons defining with said casing an intermediatechamber, a port through said fixed casing for admitting charging fluidto said intermediate chamber, said primary and secondary pistons havingdifferential areas exposed to said charging fluid and to said high andlow pressure chambers arranged in such manner that said charging fluidcauses said primary piston to develop working pressures in said highpressure chamber in excess thereof and said secondary piston maintainspressure in said low pressure chamber of lesser magnitude than saidcharging pressure and automatic means including a continuously operatingcirculating pump in circuit with said low pressure chamber and a by-passvalve in circuit with said high and low pressure chambers initiated bymovement of said primary piston within said casing for auto maticallysupplying make-up fluid to said high pressure chamber.

8. In a hydraulic actuating system, a servomotor, a servo control valve,fluid conduits connecting said servomotor with said control valve, anaccumulator having a fixed casing, said fixed casing having a firstcylindrical chamber and a primary piston reciprocable within said firstchamber, said casing having a second cylindrical chamber, and asecondary piston reciprocable Within said second chamber, a thirdchamber formed by said casing and the adjacent faces of said primary andsecondary pistons, a port through said fixed casing for admittingcharging fluid to said third chamber, said primary and secondary pistonshaving differential areas arranged in such manner that said chargingfluid causes said primary piston to develop high pressure workingpressures in said first chamber and said secondary piston maintainspressure in said second chamber of lesser magnitude than said chargingpressure, and high pressure fluid conduits connecting said first chamberwith said servomotor and with said servo control valve.

9. In a hydraulic actuating system, a servomotor, a servo control valve,fluid conduits connecting said servomotor with said control valve, anaccumulator, having a fixed casing, said fixed casing having a firstcylindrical chamber and a primary piston reciprocable within said firstchamber, said casing having a second cylindrical chamber and a secondarypiston .reciprocable within said second chamber, a third chamber formedby said casing and the adjacent faces of said primary and secondarypistons, a port through said fixed casing for admitting charging fluidto said third chamber, said primary and secondary pistons havingdifferential areas exposed to said charging fluid arranged in suchmanner that said charging fluid causes said primary piston to develophigh pressure working pressures in said first chamber and said secondarypiston maintains pressure in said second chamber of lesser magnitudethan said charging pressure, high pressure fluid' conduits connectingsaid first chamber with said servomotor and with said servo controlvalve, and automatic means including a circulating pump forautomatically supplying make-up fluid to said firs-t chamber on the highpressure side of said primary piston.

10. In a hydraulic actuating system, a servomotor, a servo controlvalve, fiuid conduits connecting said servomotor with said controlvalve, an accumulator having a fixed, casing, said fixed casing having afirst cylindrical chamber and a primary piston reciprocable within saidfirst chamber, said casing having a second cylindrical chamber and asecondary piston reciprocable within said second chamber, a thirdchamber formed by said casing and the adjacent faces of said primary andsecondary pistons, a port through said fixed casing for admittingcharging fluid to said third chamber, said primary and secondary pistonshaving differential areas arranged in such manner that said chargingfluid causes said primary piston to develop high pressure workingpressure-s in said first chamber and said secondary piston maintainspressure in said second chamber of lesser magnitude than said chargingpressure, high pressure fluid conduits connecting said first chamberwith said servomotor and with said servo control valve, a return conduitfrom said servomotor to said. control valve and said accumulator,automatic means including a continuously operating circulating pump anda by-pass valve initiated by movement of said primary piston within saidcasing for automatically supplying make-up fluid to said first chamberon the igh pressure side of said primary piston.

11. An accumulator device for receiving charging power from a compressedgas and supplying fluid power to a motor, comprising a high pressurefluid chamber having a primary piston reciprocable therein for varyingthe capacity of said high pressure chamber, a low pressure fluid chamberhaving a secondary piston reciprocable therein for varying the capacityof said low pressure chamher, an intermediate chamber formed between andopen to opposed faces of said primary and secondary pistons adapted tobe supplied with a compressed gas at a predetermined pressure, saidopposed faces of said primary and secondary pistons having differentialareas exposed to said compressed gas and the opposite faces of saidpistons having differential areas exposed to the fluid in saidrespective chambers whereby said primary piston develops high pressurefluid in said first chamber for supplying fluid power to said motor andsaid secondary piston develops low pressure fluid in said secondchamber, pump means normally circulating fluid at low pressure throughsaid second chamber, and by-pass valve means initiated by loss of fluidfrom said high pressure supply to said motor for automaticallyreplenishing said fluid by supplying liquid at high pressure from saidpump means to said first chamber.

References Cited in the file of this patent UNITED STATES PATENTS2,673,527 Ashton et al Mar. 30, 1954

